Production of nitric acid and liquid nitrogen tetroxide



Jan. 29, 1935. N. cARo ErAL '1,989,267

PRODUCTION OF NITRIC ACID AND LIQID NITROGEN kTETROXIDE Filed July 5, 1929 ATTORNEYS Patented Jan. 29, 1935 i UNITED vslurss PATENT `orties PRODUCTION OF NITRIC ACID AND LIQUID NITROGEN TETROXIDE Nikoaem om and Albrt Rudolf Frank, Berlin,

and Rudolf Wendlandt and Thomas Fischer, Piesteritz, near Wittenberg, Germany Application July 5, 1929, Serial No. 376,266 In Germany November 9, 1926 12 Claims. (Cl. 23?-160) This inventionrelates to a process for converttration. In this manner, tetroxide-containing ing the whole of the nitric oxide (NO), produced acid of very low water vapour pressure is nally by combustion of ammonia, to highly'concenseparated from lthe oxidized gases. y trated nitric acid or to liquid nitrogen tetroxide In the third phase nitrogen tetroxide or highly 6 Without utilizing sulphuric acid to bind an excess concentrated nitric, acid isproduced, for example v5:

of water and without distillation of dilute nitric by cooling the gas to a low temperature, if necesacid: sary in stages; Also substances may be em- Htherto, this .conversion has not been effected ployed-ifv lnecessary in stages-which lower the in a satisfactory manner. It has been proposed vapour-pressure of the -tetroxide or have absorb- 10 to. dry the gases and to separate the water as ing properties.I Substances which are dissolved 10-1 free from acid as possible. It has however not in the condensed nitrogen'tetroxide, lower the been found rpossible to effect this waterseparavapour pressure of the liquid. Solvents which tion satisfactorily because either a'large' portion dissolve the tetroxide are also adapted to lower ofthe yield is converted into aqueous nitric acidl the vapour pressure of the tetroxide. Solid adlfor a considerable proportion of the nitrogen comsorption .agents lower the .vapour pressure' of the 15-r` pounds is lost in the water.l This is the case tetroxide by adsorption. An example of diseven when the water, as poor in acid as possible,v solved substances is nitric acid. Nitric acid is is removed immediately after leaving'theappa` also an exampleof vasolvent'. An example of a ratus used for the combustion of the ammonia, solid adsorptionagent is silica gel. We Wish and is especially so in the case of concentrated it to beunderstood'that in the third phase ac- 20 mixtures or in mixtures enriched with oxygen. cording to the present invention an excess of The losses are particularly serious when the s epwater is impossible, and therefore we make no eration of the water takes place only afterV the" claim to any Vprocess for eliminating water from heat of the nitric oxide mixture has been utilized the liquid, or dissolved or adsorbed products of in a waste heat boiler. The preparation: ofthe the third phase ori'rom any mixture contain- 25 nitrogen tetroxide is rendered still more dicult `ing the liquid andthe dissolved or adsorbed prodas the gas mixture obtained is not dry. ucts' of the third phase. The gas mixture may It has now been found in accordance with this be liqueed, and then. the residual gas mixture invention thatthe above mentioned disadvanwashed with a solvent or adsorbed. The liquetages may be avoided if a portion only of the faction, "solution or adsorption may take place steam is withdrawn without allowing any conat low temperature, ii necessary, in several siderable oxidation prior to or during this rst stages, and also solid oxides of nitrogen may be Working phase, so that in the second phase the frozen out. Dissolved or adsorbed or solid niresidual water separates as nitric acid, during trogen tetro-xide may be added as such, or after 85 of after the oxidation of the nitric oxide, and melting or Vaporizing, toy the liquid nitrogen in the third Phase nitlogerl tetl'OXde 0I' highly tetroxide, or to the crude mixture of nitrogen concentrated nitric acid is produced. v tetroxide and nitric acid.

At first only a portion of the steam is separated When it is only a question of drying, the water by cooling without allowing any considerable ox separation in the iirst phase may be extensive.

4|)` idation of the nitric oxide mixtureto take place. For the production of highly concentrated nitric 40" As the whole of the steam is not to be removed acid suincient Water vapour can be allowed to the separation can take place much more rapidly enter the second phase so that the condensates and at a high discharge temperature. Both of the second and third phases which may be these circumstances tend to prevent the oxidation united together or employed for the mutual irri- 0f the ntl' OXde and the abSOIption of nitrogation or scrubbing and absorptiongive a mixture 5 gen oxides in the separated water. Addition of suitable for .the production of highly concen oxygen, if necessary, takes place'only after the trated nitric acid. In many-cases the water rst phase. vapour and nitrogen tetroxide may pass to the In the second phase the residual water vapour second phase in approximately equimolecular is separated during or after the oxidation of proportions. The union of the condensates from 50 the nitric` oxide (NO). The oxidation of NO the second and thirdk phases may be effected, for to NO2 as Well as the separation of the acid is example, continuously," in any. suitable manner; promoted by decreasing the temperature. The" a condensate system maybe irrigated or the condensate obtained during` ythe Vsecond phase like by-its condensate or by the condensate from 56'- may be collected inone or two stages'ofconcenanother systemvby means of a cycle, direct cur- 55- rent, counter current, etc. The crude mixture of nitrogen tetroxide and nitric acid is converted into highly concentrated nitric acid of any desired concentration, e. g. 98-100% nitric acid free from tetroxide can be produced, by using oxygen under pressure preferably at increased temperature. It is obvious that weaker acids may be produced, the water content varying according to the special purposes for which it is required and the conditions used.

As the condensates from the second and third phase together give a crude mixture adapted for working up to highly concentrated nitric acid, the condensation may take place in one phase, the second and third phases being combined.

Special advantages are obtained by the use o1 increased pressure; the whole plant may work at increased pressure, or the ammonia oxidation may be carried out at atmospheric pressure this being in many cases a special advantage of this invention, the gas mixture being compressed only after leaving the combustion apparatus or only after the first water separation or even only after the separation of the acid is complete. The technical diiiculties of thiscompression are avoided when it is carried out in a turbo-compressor. The expansion of the gases remaining after the absorption is then carried out preferably in an expansion turbine which is coupled with the compressor. Pressures of for example 5 to 10 atms. may be employed. It is especially advantageous to use the end gas at increased pressure, if necessary by changing its temperature by passing it through'a heat-exchanger prior tothe expansion and with work done during the expansion. The increased pressure may be used in several stages.

Oxygen-containing compressed residual gas may enter pressure spaces to which condensates from the second and third phase (or crude mixtures of nitrogen vtetroxide and nitric acid or condensate obtained during the compression) may be admitted. Very high pressures may also be used, for example 50 to 200 atms. In .this manner the residual gas may be worked up by means of pressure into highly concentrated nitric the quantity of nitric oxide remaining in the gaseous state in the waste gas can be reduced at will so that it may be neglected in the working up of low percentage gases, or the said nitric oxide may be washed with water, for example with condensed water coming from the rst phase, and converted by that water and the oxygen contained in the end gas into aqueous nitric acid, if there should be any demand for the same.

The details of the method and the temperature conditions depend upon the concentration, and the steam and oxygen content of the nitric oxide mixture, with high percentage mixtures from the combustion of ammonia with pure oxygen, if desired with the addition of steam, the gas discharge temperature of the rst phase may be, in certain circumstances, above 100 C. sometimes even considerably above. With gases from a normal ammonia combustion with atmospheric air at atmospheric pressure this temperature might be much lower for example 45 C. The conditions for the other phases diier similarly.

The application of the process of this invention is not limited to the ammonia combustion mixtures but extends to all moist nitrous gases which are treated in a corresponding manner. The principal value of the process is thepossibility of producing as much highly concentrated nitric acid as is required or a crude mixture which is capable of being converted directly into highly concentrated nitric acid.

In all the processes for the production of nitric acid as described the residual gas of the condensation can obviously be utilized or worked upto nitrogen or oxygen according to its composition.

The following example which refers to the accompanying diagrammatic drawing illustrates one method of carrying the invention into eiect:

Referring to Figure 1, a nitrogen oxide mixture is prepared, for example, by the oxidation of ammonia in contact burner or ammonia oxidizer 1. This gas mixture passes through the tube 2 into a heat exchanger or cooler 3.' The steam generated in the heat exchanger 3 is led' through the pipe 5 to the place where it is to be employed. The gas mixture passes into a con. denser 4 after leaving the heat exchanger 3. The water vapour contained in the gas mixture is partially separated in said condenser 4, for example by water cooling and, until this water separation has taken place, the gases are .given no oxidation space, 1/3 of the water vapour re'- sulting from the combustion of ammonia according to the equation' is left in the gas mixture and the excess of the water vapour (which has resulted from ammonia or which has otherwise gained access to the nitrogen oxide mixture) is condensed and drawn oii,V practically free from acid through the tube' '7. The water vapour remaning in the gas is separated, during or after the oxidation of the nitric oxide, as aqueous, (possibly nitrogentetroxide-containing) nitric acid. The gases pass through tube 8 (if desired with the addition of oxygen or air through the tube 9) at the top or at the bottom into a cooling chamber l0, which is cooled, for example, with water and gives off the condensate formed at 11. By suitable disposition of space and cooling surface a condensate of any desired composition, for example 40% or 80% nitric acid containing nitrogen tetroxide may be formed. The gas mixture conveyed through tube 12 is now converted into liquid, (possibly nitric acid-containing) nitrogen tetroxide, N204. Cooling is effected in liqueer 13 with brine at a low temperature which gives off liquid nitrogen tetroxide at 14, which can also be drawn off at 15 combined with aqueous nitric acid as a raw mixture suitable for working up, for example into highly concentrated nitric acid.

The gas mixture may be liquefied and then washed with a solvent or adsorbed. Dissolved and adsorbed or solid tetroxide may be added directly (or after melting or gasifying) to the liquid tetroxide, or to the liqueer, or to the mixture of nitrogen tetroxide and nitric acid.

Figure 2 illustrates the means for liquefying the gas mixtures and then washing them with a` solvent, the dissolved tetroxide being added to the liqueer after gasification.

Figure 3 illustrates the means for liquefying the a gas mixtures and then fadsorbin'g them, the adsorbed tetroxide being 'added to the liqueer after gasification.

As shown Figure `2, the gas .mixture leaves the .liquefier 13 .through a pipe 16 and passes into a column 17, in which the nitrogen tetroxide is dissolved by a solvent (a `knovvn'examp'le o'fa good #solvent is vconcentrated nitric acid, especially highly concentrated nitricacid) the end ygas escaping through the pipe 18. The dissolved tetroxide can be removed through the pipe 19, or "it can pass through the pipe 2l, (which is provided with a val-ve and is connected with the pipe 19), and flow into the gas extractor 22. The dissolved tetroxide is gasified in the gas extractor 22 and the gaseous tetroxide is supplied to the liqueer 13 through the pipe 23. rlhe 4column 17 is cooled with brine, which also cools the liquefier 13.

'Ihe nitric acid is introduced into the column 17 through the inlet 30.

Referring to Figure 3, the gas passes out of the liquefier 13 through 16, into an adsorber 24 and escapes at 25, whilst the previously employed adsorber 26 is freed .from gas by heating, the gas leaving the adsorber 26 through the lead 23. 24 and 26 operate alternately in known manner (a large number of various adsorbers connected in another manner may also be employed. The cooling of the adsorbers is effected with brine, such as is employed for the liquefier 13 or with brine at a lower temperature.

The method of carrying the invention into etfect described in the examples is suitable, for example, for Working up any ammonia combustion mixtures, such as can be obtained from ammonia and atmospheric air or air rich in oxygen or from ammonia and oxygen in various concentrations. Thus catalytically oxidized mixtures of one part by volume of NH3 with 1.5 to 2.5 parts by volume of oxygen, with or without the addition of steam in any desired proportion, for example 35 volume NH3 in oxygen maybe Worked up by this method With about 1 cu. metre total condensation space per ton of nitrogen converted per day at atmospheric pressure. Mixtures obtained from the combustion of ammonia with atmospheric air are Worked up according to this method preferably under increased pressure, for example at 3 to 10 atms. etc. The pressure in this case may be extended over the Whole plant or only overl parts thereof; also when burning with oxygen, pressure may, for example, be employed at the end etc. On the other hand even the low percentage ammonia combustion mixtures obtainable with atmospheric air can be Worked up in this manner at atmospheric pressure without previous liquefaction, for example by constructing the apparatus illustrated in Figures 2 or 3 in a suitable manner and connecting them at 12.

We claim:-

l. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water-vapor, Which comprises condensing a portion of the water-vapor to form Water substantially free of nitric acid, removing said condensate, condensing the residual Water vapor and a portion of the nitrogen oxides to form nitric acid, and cooling the residual gases to low temperatures to obtain a further condensate.

2. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, which comprises condensing a portion of the Water vapor to form water substantially free of nitric acid, removing said condensate, condensing the residual Water vapor 4and a portion of the nitrogen oxides .to form nitric acid, and then lique- -fying 'the residual nitrogen oxides. K

` 3. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, which comprises condensing a portion of the Water vapor to form Water substantially free of nitric acid, removing said condensate, condensing the residual Water vapor and a portion of the nitrogen oxides to form nitric acid, and absorbing the residual gas mixture at low temperatures.

4. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, which comprises condensing a portionA of the Water vapor to form Water substantially free of nitric acid, removing said condensate, condensing the residual Water vapor and a portion of the nitrogen oxides to form nitric acid, liquefying a portion of the residual nitrogen oxides, and then absorbing the remainder with highly concentrated nitric acid, the liquefying and the absorption operations being carried out at low temperatures.

5. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, Which comprises condensing a portion of the Water vapor to form Water substantially free of nitric acid, removing said condensate, condensing the v,residual Water vapor and a portion of the nitrogen oxides to form nitric acid, liquefying the residual nitrogen oxides and combining the nitric acid and the liquefied nitrogen oxides.

6. .A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor,I

which comprises condensing a portion of the Water vapor to form Water substantially free of nitric acid, removing said condensate, condensing the residual Water vapor and a portion of thenitrogen oxides to form nitric acid, liquefying the residual nitrogen oxides, combining the nitric acid and the liquefied nitrogen oxides to form a liquid mixture thereof, and adding oxygen under pressure to this mixture to form highly concentrated nitric acid.

7. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, which comprises first condensing a portion of the Water vapor to form Water substantially free of nitric acid, removing said condensate, condensing the residual Water vapor and the residual nitrogen oxides, the condensate consisting of a liquid mixture of Water, nitric acid and nitrogen tetroxide, and adding oxygen under pressure to this mixture to form highly concentrated nitric acid.

8. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, Which comprises iirst condensing a portion of the water vapor to form Water substantially free from nitric acid, removing said condensate, adding oxygen to the resultant gas mixture, condensing the residual Water vapor and a portion of the nitrogen oxides to form nitric acid, and cooling the residual gases at 10W temperatures.

9. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, which comprises first condensing a portion of the Water vapor to form water substantially free from nitric acid, removing said condensate, adding oxygen to the resultant gas mixture, condensing the residual Water vapor and the residual nitrogen oxides, to form a liquid mixture of Water, nitric acid and nitrogen tetroxide, and adding oxygen under p-ressure to this liquid mixture.

10. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor,

which comprises condensing a portion of the Water vapor to form water substantially free of nitric acid, removing said condensate, condensing the residual Water vapor and a portion of the nitrogen oxides to form nitric acid, and cooling the residual gases to 10Wy temperatures to obtain a further condensate, said process being carried out at a pressure substantially greater than atmospheric.

11. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, which comprises condensing a portion of the Water Vapor to form Water substantially free of nitric acid, kremoving said condensate, condeming the residual water Vapor and a portion of the nitrogen oxides to form nitric acid, and cooling the residual gases to low temperatures to obtain 'a further condensate, the second condensing and the final cooling operations being carried out at a pressure substantially greater than atmospheric.

12. A process of treating gas mixtures containing nitrogen oxides, oxygen and Water vapor, which comprises condensinga portion of the water vapor to formwater substantially free of nitric acid, removing said condensate, condensing the residual Water Vapor and a portion of the nitrogen oxides to form nitric acid, and cooling the residual gases to low temperatures to obtain a further condensate, the final cooling operation being carried out at a pressure substantially greater than atmospheric.

NIKODEM CARO.

ALBERT RUDOLF FRANK. RUDOLF WENDLANDT. THOMAS FISCHER. 

